The possibility of magnetic imaging in solids has attracted considerable interest recently. NMR imaging in solids is difficult because of the broad NMR lines. One possible approach to the problem is to artificially narrow the line. Such an approach is disclosed in UK Patent Application No. 2234594.
An alternative to line narrowing has been described by Cottrell et al. in their paper entitled "NMR imaging of solids using large oscillating field gradients" (Meas. Sci. Technol. 1, 1990, 624). This paper discloses the use of large oscillating field gradients to dominate the homogeneous dipolar broadening. A single 90.degree. excitation pulse is applied at the time when the field gradient passes through zero and a gradient echo is produced after one complete gradient cycle. Because the 90.degree.pulse is applied at the moment of zero gradient, the RF power requirements are quite modest. The imaging scheme disclosed in this paper used back projection.
Although back projection methods have been conventionally used in solid state NMR imaging, it would be advantageous to use two dimensional Fourier transform (2DFT) techniques since these might be expected to lead to an improvement in image quality.